The amount of heat generated in an electrochemical cell during the discharge process may affect cell performance, and if excessive may result in serious hazards. To achieve the desired cell performance and maintain safe operation, an understanding of thermal behavior is important with regard to the rates of discharge and non-electrochemical reaction heats. Therefore it is desirable to measure the total internal heat during battery operation. A sensitive and precise calorimeter capable of measuring a very small amount of heat is essential to accurately quantify the thermal behavior of battery operation.